In Europe it's common for regional rail systems to get ridership comparable to that of the subway in the central city. But in America, this is unheard of. One reason for the discrepancy is land use: American commuter rail stations are typically surrounded by parking, while in the Paris region you see a different pattern with ample development next to suburban train stations.

In the U.S., regional rail is mostly good for one type of trip: the commute. But in Paris, regional rail is oriented toward all types of trips, and people ride throughout the day, not just at rush hour. One key to success is running frequent, predictable service all day long.